Erm... if I remember right Tyranids, Necrons and Chaos Space Marines cannot use the Daemonhunters Adversaries rules, meaning no, Tyranids cannot be possessed by Daemons.

Originally Posted by Andusciassus

If you translate the breasts from the FW-greater Daemon, the size of a Defiler, I don't think there would be any problem fitting six such on it.
If you like them larger, sure they might not fit, but I think the Defiler would look a bit... iffy. Like Dolly Parton 40 000. Not really my cup of tea.